C-kit is a receptor tyrosine kinase expressed on the surface of mast cells, to which stem cell factor (SCF) is a ligand. Aberrant c-kit signaling is believed to be a mediator of certain autoimmune diseases. Binding of SCF to the c-kit receptor mediates various functions of the mast cell. As an important mediator of mast cell function, c-kit is thought to also play a role in pathologies associated with mast cells (MC). C-kit functions through mast cell generation, which plays an important role in triggering autoimmune diseases. Mast cells are tissue elements derived from a particular subset of hematopoietic stem cells that express CD34, c-kit and CD13 antigens (Kirshenbaum et al., Blood 94:2333-2342, 1999 and Ishizaka et al, Curr. Opinion Immunol. 5:937-943, 1993). Mast cells are characterized by their heterogeneity, not only regarding tissue location and structure but also at the functional and histochemical levels (Aldenberg and Enerback, Histochem. J. 26:587-596, 1994; Bradding et al., J. Immunol. 155:297-307, 1995; Irani et al., J. Immunol. 147:247-253, 1991).
Mast cells are thought to participate in the destruction of tissues by releasing various proteases and mediators categorized into three groups: pre-formed granule associated mediators (histamine, proteoglycans, and neutral proteases), lipid-derived mediators (prostaglandins, thromboxanes, and leucotrienes), and various cytokines, including IL-1, IL-2, IL-3, IL-4, IL-5, IL-6, IL-8, TNFα, GM-CSF, MIP-1a, MIP-1b, MIP-2 and IFNγ. The liberation of these mediators induces and activates various components of immune response involved in autoimmune diseases, and also promotes the tissue destruction process.
Activation of the auto-immune response is postulated to be caused by, or stimulated from, the degranulation of mast cells. Immature MC progenitors circulate in the blood stream and differentiate in the tissues. These differentiation and proliferation processes are influenced by various cytokines. Stem Cell Factor (SCF) and IFNγ are two cytokines which are important in influencing such processes. The SCF receptor is encoded by the proto-oncogene c-kit, which belongs to the type III receptor tyrosine kinase subfamily (Boissan and Arock, J. Leukoc. Biol. 67:135-148, 2000), along with PDGF and cFMS. Ligation of c-kit receptor by SCF induces its dimerization followed by its transphosphorylation, leading to the recruitment and activation of various intracytoplasmic substrates. IFNγ is another cytokine secreted by mast cells. It has been reported that IFNγ is responsible for major histocompatibility complexes associated with autoimmune diseases (Hooks et al., New England J. of Med., 301:5-8, 1979). These activated substrates induce multiple intracellular signaling pathways responsible for cell proliferation and activation (Boissan and Arock, 2000).
TNF is another cytokine produced by mast cells. More recently, it has been reported that the TNF produced by mast cells is involved in the pathogenesis of auto-antibody mediated vasculitis (Watanabe et al., Blood 11:3855-3866, 1994). Mast cells were also shown to control neutrophil recruitment during T-cell mediated delayed-type hypersensitivity reactions through TNF and macrophage inflammatory protein 2 (MIP-2). Accordingly, c-kit regulation may be useful in various types of inflammation including without limitation, rheumatoid arthritis, severe asthma, allergy associated chronic rhinitis, and the like.
Mast cells have also been implicated in liver allograph rejection (Yammaguchi et al., Hematology 29:133-139, 1999) and in liver fibrosis, where hepatic stellate cells produce the SCF that recruits the mast cells (Gaca et al., J. Hematology 30:850-858, 1999). These observations suggest that c-kit kinase inhibitors may help prevent organ rejection and fibrosis. Some possible related c-kit mediated therapeutic indications include idiopathic pulmonary fibrosis (IPF) and scleroderma. Mast cells have also been implicated in the pathology of multiple sclerosis (Secor et al., J. Experimental Medicine 191:813-822, 1999), and ischemia-reperfusion injury (Andoh et al, Clinical & Experimental Immunology 116:90-93, 1999) in experimental models using mice with mutant kit receptors that are deficient in mast cells. In both cases, the pathology of the diseases was significantly attenuated relative to mice with normal c-kit and mast cell populations. Thus, the role of mast cells in these diseases suggests that c-kit modulators might be useful therapeutics.
C-kit signaling is also important for fetal gonadal development, and plays a role in adult fertility (Mauduit et al, Human Rep. Update 5: 535-545, 1999). Spermatogenesis is inhibited through a reduction of c-kit activity in c-kit signaling through the PI3 kinase pathway (Blume-Jensen et al, Nature Genetics 24:157-162, 2000). C-kit expression has been observed to be lower in sub-fertile testes than in normal testicular tissue (Feng et al, Fertility and Sterility 71:85-89, 1999). C-kit signaling is also important for oogenesis and folliculogenesis (Parrott and Skinner, Endocrinology 140:4262-4271, 1999). These reports suggest that modulation of c-kit enzymatic activity may be a method to reduce both male and female infertility.
While various groups have published on inhibitors of c-kit kinase, disclosing various chemical compounds, including 2-phenylamino-imidazo[4,5-h]isoquinolin-9-ones (Snow, R J et al, J. Med. Chem. 2002, 45, 3394), pyrazolo[3,4-d]pyrimidines (Burchat, A F et al, Bioorganic and Med. Chem. Letters 2002, 12, 1987 and Hanke, J H et al, J. Biol. Chem. 1996, 271, 695), pyrrolo[2,3-d]pyrimidines (Altmann, E et al, Bioorganic and Med. Chem. Letters 2001, 11, 853), anilinoquinazolines (Wang, Y D et al, Bioorganic and Med. Chem. Letters 2000, 10, 2477), imidazoquinoxalines (Chen, P. et al, Bioorganic and Med. Chem. Letters 2002, 12, 3153), PCT publication entitled, “Methods of Modulating C-kit Tyrosine Protein Kinase Function with Indoline Compounds” and PCT publication entitled, “Use of Tyrosine Kinase Inhibitors for Treating Autoimmune Diseases”, none of these groups describe the compounds of the present invention, and particularly as modulators of kinase enzymes such as c-kit, and useful for the regulation of autoimmune disease(s), allergies, asthma, cancer and the like.